Copolyamides of the basic units caprolactam, lauriclactam and 11-aminoundecanoic acid are known from DOS No. 1,595,591. In melt form, these ternary polyamides show high bond strength which is used in the textile industry for heat-sealing fabrics. In addition to high bond strength, these copolyamides show high resistance to solvents of the kind used for dry-cleaning textiles, and to the washing temperatures of up to about 80.degree. C normally encountered in the textile industry. Unfortunately, this resistance is largely governed by a high content of lauriclactam and/or 11-aminoundecanoic acid. Although the resistance of the copolyamides to washing at elevated temperatures increases with increasing content of these basic units, their melting temperature is also increased with the result that conventional copolyamides cannot be used for heat-sealing temperature-sensitive substrates such as leather, temperature-sensitive natural and/or synthetic materials, non-woven fabrics, felts, tufted fabrics and the like. Substances melting below about 115.degree. C, below 110.degree. C or even below 105.degree. C, are required for heat-scaling temperature-sensitive substrates of this kind.